High-power Ho Research Articles

High-Power Ho-Doped Sesquioxide Ceramic Laser In-Band Pumped by a Tm-Doped All-Fiber MOPA

We report on a high-power Ho:Y2O3 ceramic laser in-band pumped by a homemade Tm-doped all-fiber MOPA at 1941 nm. The Ho:Y2O3 ceramics fabricated by vacuum sintering and hot isostatic pressing present uniform ceramic grain and high optical homogeneity. The 24.6 W output power at ∼2117 nm is successfully achieved by exploiting the advantages of in-band pumping technique, which to our knowledge is one order of magnitude higher than the previous results obtained from the Ho-doped sesquioxides ceramic lasers, indicating the power scalability of sesquioxides ceramic compared to other bulk materials in high-power laser.

Efficient High-Power Ho:YAG Laser Pumped by Dual-End-Diode-Pumped Tm:YLF Laser

We report a Ho:YAG (Ho-doped yttrium aluminum garnet) laser pumped by a dual-end-diode-pumped Tm:YLF (Tm-doped yttrium lithium fluoride) laser to obtain an efficient experimental device with high output-power characteristics. We study the influence of the specific values of the output coupling mirror transmittance, the resonant cavity length, and the radius of curvature of the output coupling mirror on the Ho:YAG laser output characteristics. Under optimum experimental conditions, under which the output coupling mirror transmittance was 30%, the resonant cavity length was 25 mm and the output coupling mirror radius of curvature was 300 mm, and the maximum pumping power of the dual-end-diode-pumped Tm:YLF laser was 15.2 W. We obtain an efficient high-power 2.122-μm laser output of 7.98 W from the Ho:YAG laser. The optical-to-optical conversion efficiency is 52.5%, and the beam quality factor figures are Mx2 = 2.89 and My2 = 2.97.

Mini-percutaneous nephrolithotomy with high-power holmium YAG laser in pediatric patients with staghorn and complex calculi

Shock wave lithotripsy (SWL) is the treatment of choice for most cases of renal lithiasis in children. Some cases, however, are refractory to SWL and may be associated with anatomic and metabolic changes or a large stone burden. In these circumstances, mini-percutaneous nephrolithotomy (mini-PCNL) is an option. The aim was to assess the safety and efficacy of high-power holmium YAG (Ho:YAG) laser in mini-PCNL for staghorn calculi. The clinical records relating to 35 mini-PCNLs (Table) performed between January 2008 and December 2012 in 33 patients (27 boys and 6 girls; mean age 7 years, range 2-18 years) were retrospectively reviewed. Twenty-two (66.7%) of the patients had undergone a previous SWL (28.6% three sessions). The mini-PCNL puncture technique used involved fluoroscopic guidance with the C arm at 0-90° in the supine position. An 18F tract was used. Stone fragmentation was performed with a high-power Ho:YAG laser (Lumenis 100W). Ten of the mini-PCNLs (28.6%) were right sided, and 25 were left sided (71.4%). Stones were located in the lower calyceal group in 64% of patients and in the renal pelvis in 50%. The mean stone size was 4.46cm(2) (range 3-13.20cm(2)). The number of stones varied between one and 20, and 83.3% were radiopaque. The laser was set at 70W (range 50-100W) (3.5J/pulse with a frequency of 20pulses/s). The mean surgical time was 150min. In 78% of patients, complete stone clearance was achieved, and the overall stone-free rate rose to 85% when residual stones were treated with either SWL or retrograde intrarenal surgery. No perioperative complications were seen. There are few reports in the literature concerning the use of a high-power laser for treatment of complex stones and the few that do exist relate to adults have similar results, showing it to be highly effective and safe, with low morbidity. Some limitations of the present study must be acknowledged. It was retrospective and a relatively small number of patients were included. However, randomized prospective studies are required to confirm our findings and conclusions. In the pediatric population, mini-PCNL with high-power Ho:YAG laser is feasible and safe and represents the technique of choice for complex renal stones.

High-Power Dual-End-Pumped Actively Q-Switched Ho:YAG Ceramic Laser**Supported by the National Natural Science Foundation of China under Grant Nos 61308009, 61405047 and 50990301, the China Postdoctoral Science Foundation Funded Project under Grant No 2015T80339, the Fundamental Research Funds for the Central Universities under Grant No HIT.NSRIF.2015042, and the Science Fund for Outstanding Youths of Heilongjiang Province under Grant No JQ201310.

We present a high-power Ho:YAG ceramic laser pumped at 1908 nm. Using a dual-end-pumped structure, the maximum continuous-wave output power of 48 W is obtained, corresponding to a slope efficiency of 70.4% with respect to the absorbed pump power. At actively Q-switched mode, the maximum average output power of 46 W and the minimum pulse width of 21 ns are achieved at a pulse repetition frequency of 20 kHz, corresponding to a peak power of approximately 109.5 kW. In addition, the beam-quality M2 factor is found to be 1.4 at the maximum output power.

High-power Ho:YAG laser wing-pumped by a Tm:fiber laser at 1933 nm

We report on the high-power and efficient operation of a Ho:YAG laser wing-band-pumped by a Tm:fiber laser at 1933 nm. Using an output coupler of 10% transmission, maximum continuous-wave (CW) output power of 24.2 W at 2124 nm was generated under 42.6 W of absorbed pump power, corresponding to slope efficiency with respect to absorbed pump power of 57.6%. The operating wavelength of the Ho:YAG laser centered at 2092 or 2124 nm depending on different resonator designs. Prospects for further improvement in laser performance with this wing-pump configuration are discussed.

In-Band Pumped High Power Ho:YAG Ceramic Laser by a Tm:YLF Laser

We demonstrate a high power Ho:YAG ceramic laser resonantly pumped by a Tm:YLF laser at 1908 nm. The lasing characteristics of a 1.0 at.% Ho3+-doped YAG ceramic are investigated and compared with different output couplers. By using an output coupler of 50% transmission and 100 mm radius of curvature, a 26.8 W continuous wave is obtained at 2091 nm, corresponding to a slope efficiency of 57.9% and an optical to optical efficiency of 55.8% with respect to the absorbed pump power.

High power Ho:YAG laser pumped by two orthogonally polarized Tm:YLF lasers

High efficient and high power 2 $$\upmu $$ m room temperature Ho:YAG laser resonantly dual-end-pumped by two orthogonally polarized diode-pumped Tm:YLF lasers at 1.91 $$\upmu $$ m was demonstrated. A maximum continuous wave output power of 61.9 W was generated, corresponding to the slope efficiency of 63.9 % with respect to the incident pump power and optical-to-optical conversion efficiency of 59.9 %. At 20 kHz of the pulsed repetition frequency, we achieved a less than 25 ns FWHM pulse, with the maximum output energy per pulse of 2.84 mJ as well as a peak power of approximately 113.6 kW. A beam quality of $$M^{2}<$$ 1.6 was achieved.

E132 Percutaneous nephrolithotomy with high-power Ho: YAG laser for complicated renal calculi

E132 Percutaneous nephrolithotomy with high-power Ho: YAG laser for complicated renal calculi

High- vs Low-power Holmium Laser Lithotripsy: A Prospective, Randomized Study in Patients Undergoing Multitract Minipercutaneous Nephrolithotomy

To determine the efficacy and safety of high-power holmium: yttrium aluminum-garnet (Ho:YAG) laser lithotripsy for multitract modified minimally invasive percutaneous nephrolithotomy (MPCNL) in the treatment of patients with large staghorn renal calculi. A randomized, prospective study was conducted. Two-hundred seventy-three consecutive patients (291 renal units) with large staghorn renal calculi were randomized to undergo multitract MPCNL with 30-W low-power or 70-W high-power Ho:YAG laser lithotripsy. Both groups were compared in terms of perioperative findings and postoperative outcomes, including procedure time, stone-free rate, length of hospital stay, transfusion rates, renal function recovery, and other complications. The average patient age was 49.2 years (range 22-73) and mean stone size was 5.54±0.7 cm. The 2 groups had some comparable perioperative findings and outcome, including tracts required per operated renal unit (n), blood loss, postoperative fever, postoperative hospital stay, stone-free rate, and improvement of operated renal function. The operation time in the high-power group was significantly shorter than that in the low-power group (129.20±17.2 vs 105.18±14.2, P<.01). A combination of multitract MPCNL and high-power Ho:YAG laser lithotripsy can greatly decrease the operative time without increasing the intraoperative complications or delaying postoperative renal function recovery when compared with low-power Ho:YAG laser lithotripsy.

Efficient high-power Ho:YAG laser directly in-band pumped by a GaSb-based laser diode stack at 1.9 μm

An efficient high-power Ho:YAG laser directly in-band pumped by a recently developed GaSb-based laser diode stack at 1.9 µm is demonstrated. At room tempera- ture a maximum continuous wave output power of 55 W at 2.122 µm and a slope efficiency of 62% with respect to the incident pump power were achieved. For narrow linewidth laser operation a volume Bragg grating was used as output coupler. In wavelength stabilized operation a maximum out- put power of 18 W at 2.096 µm and a slope efficiency of 30% were obtained. In this case the linewidth is reduced from 1.2 nm to below 0.1 nm. Also spectroscopic proper- ties of Ho:YAG crystals at room temperature are presented.

Efficient holmium-doped fluoride fiber laser emitting 21 µm and blue upconversion fluorescence upon excitation at 2 µm

We demonstrate a highly efficient and high power Ho(3+)-doped fluoride glass fiber laser that is resonantly pumped with a Tm(3+)-doped silicate glass fiber laser operating at 2.051 µm. The laser operates at 2080 nm and generated 6.66 W at a slope efficiency of 72%. We observe strong visible upconversion fluorescence centered at a variety of wavelengths including 491 nm which results from three sequential energy transfer upconversion processes; the fluorescence to pump energy ratio for this emission is one the largest reported to date.

70 W Holmium:Yttrium-Aluminum-Garnet Laser in Percutaneous Nephrolithotomy for Staghorn Calculi

To investigate the safety and efficacy of the high-power (70 W) holmium laser in percutaneous nephrolithotripsy (PCNL) for staghorn calculi. From December 2004 to March 2008, 438 consecutive patients (456 renal units) with > or =4-cm staghorn stones underwent PCNL with a pulsed holmium:yttrium-aluminum-garnet (Ho:YAG) laser using a 1000-microm end-firing optical fiber. For the first 106 patients (group A; average stone size 5.6 +/- 0.8 cm), a 30 W (3.0 J/pulse; 10 pulse/sec) laser was used, whereas for the other 332 patients (group B; average stone size 5.8 +/- 0.8 cm), the laser power was set at 3.0 J/pulse with a frequency of 20 pulses/sec. For stones in a calix visible with the nephroscope but unreachable with a laser, the mucosa of the calix was split with a 100 W holmium laser to fragment the stones further. Moreover, a porcine model for assessing the safety of the high-power holmium laser was developed. All patients had successful PCNL. The average lithotripsy time in group B was significantly shorter than that in group A (44 +/- 11.5 minutes vs 69 +/- 14.8 minutes; P < 0.05). No patient had a severe complication. In addition, 39 patients underwent calix splitting with no hemorrhage during or after the operation. The glomerular filtration rate of the treated kidney, reexamined 6 months after the operation, had improved greatly (45.12 vs 31.91 mL/min; P < 0.05). Pathologic evaluation of porcine kidneys exposed to high-power laser firing showed no damage. The high-power Ho:YAG laser enhances lithotripsy efficacy by "vaporizing" and "bursting" the stone quickly, reducing lithotripsy time significantly. This is an effective and safe treatment for patients with large renal stones.

Eyesafe Lasers and Their Applications. Mid-Infrared Semiconductor Lasers.

Considerable progress has been made in mid-IR semiconductor lasers in terms of maximum operating temperature and output power. Antimonide-based type-I quantum-well lasers have exhibited cw operation at 2.0 μm up to 400 K, at 2.7μm to 234 K, at 3.5μm to 175 K, and at 3.9 μm to 128 K. 4-μm lasers pumped by 1-μm diode laser arrays have yielded peak power of 2 W and average power of 240 mW at 92 K. Diode lasers utilizing type-II transitions have exhibited pulsed operation between 2.8 and 4.3 μm, with maximum operating temperature of 255 K at 3.2 μm. Type-II lasers pumped by a high-power Ho:YAG laser have operated pulsed up to 350 K at 3.2 μm and 285 K at 4.1 μm. Quantum cascade lasers emitting at - 5 μm or - 8 μm have operated pulsed up to 320 K and cw to 140 K.

High power Ho:YAG laser ablation of intervertebral discs: effects on ablation rates and temperature profile.

As the Ho:YAG laser gained increasing importance in recent experimental and clinical investigations, this study was performed to investigate the effect of power on ablation rates and temperature during disc ablation with a high power Ho:Yag laser under simulated clinical conditions. A high power Ho:YAG laser was used to investigate the influence of increasing power from 10 to 32 Watt on ablation rate (mg) and temperature (degree C). Ablation weight was measured by a precision scale calculating the difference of the pre- and postlasing weight of the specimen after application of total energies of 1,000, 1,500, and 2,000 J. Temperatures were measured by thermoprobes, which were connected via a thermomodule to an amplifier and the signal was plotted by a computer with appropriate software. Whereas ablation rate rose almost linearly with total energy, increasing power above 20 W did not essentially improve ablation rate. Temperatures reached their highest values after application of a total energy of 500 J and did not rise further, whereas increasing power did not induce a rise in temperature. Regarding the chosen experimental setting, maximum temperatures are reached after application of 500 J, and increasing power does not induce a rise in temperature.